There is increasing interest in stereoscopic television, in which a pair of images of the same scene from closely-spaced, horizontally-adjacent viewpoints are respectively presented to the left and right eyes of a viewer so as to obtain a ‘three dimensional’ image. One popular way of using existing transmission equipment to deliver stereoscopic images is to divide each frame into two halves and to use one half-frame for the left-eye image, and the other half-frame for the right-eye image. If the frame is divided horizontally, the horizontal scale of the two images is (approximately) halved; alternatively, if the frame is divided vertically, the vertical scale is (approximately) halved. The rescaling is, of course, reversed prior to display of the image.
This modified use of a transmission system requires careful monitoring and control to avoid presenting double images to 2D viewers, or simultaneously presenting different parts of the same image to the left and right eyes of stereoscopic viewers. There is thus great commercial utility for a system that processes image files or data and determines whether conventional two-dimensional images are being distributed, or whether, and in what manner, two component images of a stereoscopic image are being sent in the same frame. It is particularly helpful if image files or data can be monitored in this way whenever they are processed or transmitted. Therefore it is highly beneficial for the method of monitoring, and the monitoring apparatus, to be simple and inexpensive, so that the monitoring process can be included at many points in a transmission chain without undue additional cost.